This invention relates to a hydraulic shock absorber and more particularly to an improved hydraulic shock absorber for a vehicle suspension wherein the hysteresis effects of the compressibility of the fluid employed in the shock absorber can either be compensated for and/or employed to change the damping characteristics as desired.
The use of hydraulic shock absorbers for damping suspension travel in vehicle suspension systems are well known. Basically, these shock absorbers control the flow to or from at least one fluid chamber in order to vary the damping characteristics. Various arrangements have been provided also so that the damping characteristics can be adjusted during the vehicle travel. Although these systems are quite effective, they have not been able to accommodate for the fact that the hydraulic fluid, although generally considered as incompressible, is not in fact incompressible. This problem is particularly acute with shock absorbers that have relatively short strokes. It has been found that a large proportion of the suspension travel is due to the compression of the hydraulic fluid used in the system. Thus, even though the control of the damping during the normal operation is accurately controlled, the total shock absorber performance can be deteriorated considerably from that which is desired because of the fact that the suspension travel during the compression of the hydraulic fluid is basically uncontrolled.
The amount of compression of the hydraulic fluid and the damping force also depends upon the speed at which the suspension elements are relatively moving and this makes it further difficult to set the shock absorber to obtain the desired damping characteristics. The effect of the compressibility provides a hysteresis effect in the operation of the shock absorber which is well known. Since this hysteresis is not controllable with the prior art type of constructions, it cannot be employed to obtain the desired damping effect with conventional type shock absorbers.
One problem with the prior art type of shock absorbers, and particularly when used for extreme conditions where performance is extremely important, such as in racing vehicles, is that the damping at the end of the stroke cannot be effectively maintained at a high value so as to permit the desired suspension travel and still effective damping throughout the entire amount of movement. By utilizing the hysteresis effect and controlling it, it is possible to obtain high damping forces throughout the entire suspension travel or at desired positions in the suspension travel.
It is, therefore, a principal object of this invention to provide an improved hydraulic shock absorber.
It is a further object of this invention to provide a hydraulic shock absorber that permits control of the effect of the compressibility of the hydraulic fluid.
It is a further object of this invention to provide an improved shock absorber that permits adjustment and control of the hysteresis effect caused by the compressibility of the hydraulic fluid.